Each year in the U.S., over 250,000 patients undergo procedures where arteries or veins are surgically connected. Invariably, there is a risk of a clot (thrombosis) forming in the vessels postoperatively. Early detection of clot formation would allow removing the clot before vessels are irreversibly blocked and is key to preventing catastrophic surgical failures. Drawbacks of existing detection devices include high false positive rates, delays in detection that limit success of salvage interventions, and patient safety risks. A device that reliably detects clot formation before total occlusion has been greatly needed for years and can dramatically improve surgical success rates, decrease morbidity and length of stay, and cut hospital costs. The economic impact of eliminating unnecessary or failed procedures associated with reconstructive thrombosis alone is estimated at up to $180 million/year in the U.S. To have a successful clot monitoring device, it is necessary to register the surgical site and acquire bloo flow data over time accurately and precisely from this location. To solve this need, we have developed EchoSure, the first simple point-of-care system for direct visualization and flow quantification of post-surgical blood vessels. EchoSure will allow nurses to noninvasively monitor patients for clot formation without specialized sonographic training. Our system's first component is a novel bio-absorbable echogenic marker implant placed adjacent to the vessels intraoperatively. The second component is ultrasound image analysis software that locks onto the unique marker signature, determines the pose of the ultrasound probe vis--vis the marker, and guides the nurse to the correct location to monitor clot formation. Doppler data is then collected to analyze blood flow over time. In this Phase I proposal, we will: 1) perform cadaver testing to optimize our navigation algorithms; 2) use a 3D probe system for ground-truth validation of algorithm accuracy; and 3) obtain in vivo proof-of-concept for the system in a realistic surgical scenario. OVERALL IMPACT: By enabling routine detection of post-operative vascular thrombosis with high accuracy before complete blockage has occurred, EchoSure will solve a problem responsible for catastrophic patient morbidity and costs. Our work will have broad impact on numerous other clinical applications where clots lead to disastrous consequences, including organ transplantation and peripheral vascular surgery.